In an electrical machine, such as for example a motor or a generator, electrical energy is converted into rotational energy or rotational energy is converted into electrical energy. The electrical machine has a rotor and a stator, the stator having a laminated core, in which electrical connectors are placed and configured as a winding. In order to insulate the conductors electrically from one another, from the environment and from the laminated core, the electrical conductors are enclosed by a main insulation. During the operation of the electrical machine, the conductors heat up as a result of the electrical currents flowing in them. The heat released in the conductors is also transferred to the main insulation and the laminated core by thermal conduction.
Because thermal decomposition of the main insulation occurs after a maximum permissible temperature is exceeded, a limitation of the temperature of the electrical machine to the maximum permissible temperature is required. After advanced decomposition, a dielectric breakdown may occur through the main insulation, which leads to a shortening of the service life of the electrical machine. In order to prevent the maximum permissible temperature from being exceeded, the laminated core is conventionally provided with cooling ducts, through which a gas, such as for example air or hydrogen, is made to flow during the operation of the electrical machine in order to cool the laminated core. However, it is disadvantageous that this only allows heat to be removed from the laminated core with low heat flow densities. The maximum power with which the electrical machine can be operated is limited by the heat that can be removed from the laminated core.